The present invention is directed to a method for inputting sheet material into a printer or copier.
In known methods for inputting sheet material, a cover sheet respectively lying at the outside is pulled from a stack of sheets in response to a start signal and is transported with a draw-in speed in the direction of a sub-section of the conveying path wherein it is conveyed with an approximately constant, rated conveying speed that corresponds to the draw-in speed.
What is disadvantageous in the known method for inputting sheet material is that the spacing between successive sheets varies. This is to be attributed thereto that the frictional connection between draw-in rollers or, respectively, draw-in belts and the sheets is not 100% assured, so that what is referred to as a micro-slip occurs. The occurring micro-slip is dependent on the paper properties such as, for example, paper thickness and surface roughness. An adjustment of the draw-in force, particularly when pulling the sheets from the stack, leads to a variation of the spacing between successive sheets. When pulling the sheets from the stack, a minimum shift of the sheets neighboring the cover sheet cannot be prevented, so that the exact position of the leading sheet edge in conveying direction is also not known upon draw-in. The result is again that a variation of the spacing between successive sheets occurs.
Over one hundred sheets per minute are printed in high-performance printers. Fluctuations of the sheet spacing between a lower and an upper limit value necessarily lead to a loss of speed when printing compared to a printing with the lower limit value. One must proceed on the basis of the poorest value when specifying the printable number of sheets per time unit. However, the user wants an unchanging printing speed that can be calculated.
European Patent Application EP 0 428 922 A2 discloses an apparatus for document processing. The conveying density is increased in that the spacing between the documents is set with the assistance of a plurality of light barriers for acquiring the position of the documents.
European Patent Application EP 0 167 091 Al discloses a separating mechanism for letter mailings. The spacing between the letter mailings can be set more exactly by taking a prescribed value for the acceleration path upon draw-in into consideration.
German Laid-Open Publication DE 27 58 007 A explains a method for controlling the haul-off event in a means for the output of separated mailings of different length. In order to increase the conveying density given letter mailings of different length, the reference edge for setting the spacing between successive letter mailings is automatically selected.
Therefore, there is a need for a simple method for inputting sheet material that enables an approximately constant sheet spacing between the successively input sheets.
The aforenoted need is satisfied by the present invention wherein, in a first aspect of the invention is based on the perception that the sheet spacing can be most simply set when drawing the sheets in, since a later correction of a spacing would result in a variation of the topical position of all following sheets. An adjustment of the spacing should be possible both when a rated spacing is downwardly transgressed as well as upwardly transgressed. Given the first aspect of the invention, the transport of the sheet is therefore delayed such that a predetermined, identical spacing between sheets transported immediately following one another derives before the sub-section is reached. The setting of the spacing between the sheets thus ensues upon draw-in of the sheets into the printer. When the draw-in speed is relatively low, then there is hardly any or no delay at all. When the draw-in speed, however, is relatively high, then the delay is longer in order to set the rated spacing. Even when the draw-in speed is lower or equal to the conveying speed, a spacing can be set by delaying the cover sheet upon draw-in when the sheets are pulled from the stack with a spacing relative to one another that is smaller then the predetermined, identical rated spacing.
The delay of the transport is a simple technical measure that, for example, can be implemented by arresting a draw-in means or by decelerating said means.
Given the method according to the first aspect of the invention, the draw-in speed is greater then the conveying speed of the sheets within the sub-section. Delay time for controlling the spacing is gained on the basis of this measure. The spacing when pulling the sheets can thus be increased and the rated spacing can also be exceeded, the pulling thus becoming more reliable since having the sheets run up onto one another is avoided. The range of control of the spacing ultimately increases when increasing the draw-in speed. run up onto one another is avoided. The range of control of the spacing ultimately increases when increasing the draw-in speed.
The number of printed sheets per time unit is not diminished due to the first exemplary embodiment of the invention.
In an exemplary embodiment of the first aspect of the invention, a pre-draw-in position at which the position of the sheet is identified is located between sheet stack and sub-section. What this measure achieves is that the position of the sheet can be employed for further control events. The varying positions of the sheets in the sheet compartment no longer has any influence on a possible variation of the sheet spacing due to the recognition of the exact position of the sheet and measures based thereon.
In a further exemplary embodiment of the first aspect of the invention, the sheet is arrested between sheet stack and sub-section and, after the expiration of a holding time, it is preferably further-conveyed with the draw-in speed. Expediently, the sheet is arrested exactly at the pre-draw-in position. The holding time is dimensioned such that the predetermined, identical spacing between the cover sheet and a previously pulled sheet of the sheet stackxe2x80x94as viewed in conveying directionxe2x80x94is established during transport of the cover sheet up to the sub-section. The holding time can be calculated by simple path/time calculations. The distance between holding position and conveyor means and the draw-in speed are thereby known. The arresting can be realized, for example, via stepping motors and/or couplings.
A second aspect of the invention is directed to a means for drawing in sheet material into a printer or copier, particularly for the implementation of a method described above. The aforementioned technical effects are thus also transferred onto the means for drawing sheet material in according to the second aspect of the invention.
In an exemplary embodiment of the second aspect of the invention, the haul-off roller acting on the cover sheet is employed, the respectively to assure a dependable draw-in, the conveyor means seizes the built sheet before the trailing edge thereof is conveyed past the haul-off roller. What this measure assures is that the haul-off roller that is usually not arranged immediately at the leading edge of the sheet stack can be enabled by the conveyor means when seizing the sheet until the sheet has been completely pulled from the sheet stack. What this prevents is that further sheets are pulled from the sheet stack by the haul-off roller before the cover sheet has been completely pulled from the sheet stack.
In an exemplary embodiment of the second aspect of the invention, the sheet position is acquired with a first light barrier immediately following the draw-in means. Dependent on a signal of the first light barrier that, for example, is generated by the interruption of a light beam by the leading edge of the sheet, the draw-in means is disconnected, so that the sheet rests in the pre-draw-in position. A second light barrier is preferably arranged approximately in the predetermined spacing in conveying direction following the first light barrier. Dependent on a signal of the second light barrier that, for example, is generated by the trailing edge of a sheet that has already been pulled, the control unit again activates the draw-in means. The sheet situated in the pre-draw-in position is thus further-conveyed with the pre-determined spacing from the preceding sheet. The draw-in speed can be measured with the assistance of the two light barriers in that the duration of the transport of a sheet between the two light barriers is measured. The point in time at which the sheet is seized by the conveyor means can be acquired from the draw-in speed, so that the draw-in means can be de-activated at this point in time. With the assistance of the draw-in speed, further, one can also calculate when the pulled sheet has a minimum spacing from the stack. When the minimum spacing has been reached, then the control-unit again activates the draw-in means, so that a next sheet is pulled. pulled. A corresponding control unit has been disclosed, for example, by DE 27 58 007 A in the field of mail processing.
The third aspect of the invention is directed to a method for inputting sheet material into a printer or copier that can be utilized in combination with the method according to the first aspect of the invention or separately as well. Multiple sheet pulls are to be prevented by the method according to the third aspect of the invention. Given multiple sheet pulls, at least two sheets at least partially overlapping one another are simultaneously pulled from the sheet stack. The result is an increased consumption of sheets and, potentially, improper prints as well. An improper print is unavoidable when the sheets are printed on both sides. A known measure for preventing multiple sheet pulls is to increase the pressing power of a haul-off means when pulling the sheets from the sheet stack. However, not all multiple or, respectively, double sheet pulls can be prevented with this measure. For example, double sheet pulls derive given poor paper quality or at cut edges that have a burr.
An object of the third aspect of the invention is to prevent multiple draw-ins given input of sheet material into a printer or copier.
This object is achieved by a method based on the consideration that two sheets adhering to one another can be separated from one another by a type of shaking motion. In the third aspect of the invention, the cover sheet, particularly when being pulled from the sheet stack, is therefore transported with a draw-in rate that repeatedly greatly varies. In the extreme case, the cover sheet is pulled in away from the sheet stack by a defined time duration in start/stop mode. Due to the multiple variation of the draw-in speed, sheets also separate from one another that would not separate from one another given a one-time variation of the draw-in speed, for example upon acceleration. A reduction of multiple sheet pulls is thus achieved by a method according to the third aspect of the invention.
When the draw-in speed varies periodically, then the draw-in speed can be varied according to a clock signal with little circuit-oriented or, respectively, software-oriented outlay.
In a further exemplary embodiment of the third aspect of the invention, the draw-in speed is only varied when multiple sheet pulls occur. The variation of the draw-in speed can be activated both by an operator as well as by a sensor unit. The variation of the draw-in speed that leads to increased wear is thus only implemented an increased number of multiple or, respectively, double sheet pulls is to be anticipated due to the paper quality. Moreover, a loss of speed when pulling the sheets in usually occurs due to the varying draw-in speed, this being only justifiable when the risk of multiple sheet pulls is in fact also established.
A fourth aspect of the invention is directed to a means for drawing sheet material into a printer or copier, particularly for the implementation of the method according to the third aspect of the invention. The technical effects cited in the third aspect of the invention are thus also transferred onto the means according to the fourth aspect of the invention.
The invention is described in greater detail below with reference to exemplary embodiments. Thereby shown are:
In an embodiment, the invention provides a method for feeding sheet material into a printer or a copier comprising the steps of pulling an outwardly lying first sheet off of a stack of sheets, transporting the first sheet at a draw-in speed towards a sub-section of a conveying path, conveying the first sheet at a conveying speed through the sub-section, delaying a pulling of an outwardly lying second sheet off of the stack until a predetermined spacing exists between first and second sheets, the draw-in speed being greater than the conveying speed, pulling the second sheet off of the stack of sheets, transporting the second sheet at the draw-in speed towards the sub-section of a conveying path, and conveying the second sheet at the conveying speed through the sub-section.
In an embodiment, the method comprises calculating a point in time at which a leading edge of the first sheet will reach the sub-section, and conveying the first sheet through the sub-section at the conveying speed from said point in time.
In an embodiment, the method comprises identifying the attitude of the first sheet at a pre-draw-in position between the stack of sheets and the sub-section, and identifying the attitude of the second sheet at a pre-draw-in position between the stack of sheets and the sub-section.
In an embodiment, the delaying step further comprises arresting the second sheet the sheet stack and the sub-section until the predetermined spacing exists between the first and second sheets.
In an embodiment, the method comprises the steps of repeating the pulling, delaying, transporting and conveying steps for subsequent outwardly lying sheets.
In an embodiment, the invention comprises an apparatus for feeding sheet material into a printer or copier that comprises at least one sheet compartment for accepting a sheet stack, a draw-in mechanism for pulling outwardly lying sheets, one at a time, from the sheet stack at a draw-in speed, at least one conveyor for receiving sheets, one at a time, from the draw-in mechanism and conveying the sheets at a conveying speed, a control unit for activating and driving the draw-in mechanism, whereby the control unit delays the activation of the draw-in mechanism for successive sheets to provide a predetermined spacing between successive sheets in the conveyor, and wherein the draw-in speed is greater than the conveying speed.
In an embodiment, a first light barrier is disposed between the draw-in mechanism and the conveyor for indicating a first position of the sheet and a second light barrier disposed downstream of the first light barrier and between the first light barrier the conveyor for indicating a second position of the sheet, the first and second light barriers being connected to the control unit and sending signals thereto indicating the time the sheet reaches the first and second positions respectively, the control unit determining the draw-in speed from the signals received from the first and second light barriers.
In an embodiment, the draw-in mechanism comprises a haul-off roller that engages each outwardly lying sheet of the stack of sheets, the draw-in mechanism further comprising a draw-in belt that transports each sheet from the haul-off roller to the conveyor.
In an embodiment, the conveyor is spaced apart from the haul-off roller by a distance that is less than a length of each sheet.
In an embodiment, the control unit deactivates the draw-in mechanism upon receipt of a signal received from the first light barrier.
In an embodiment, the control unit activates the draw-in mechanism upon receipt of a signal from the second light barrier.
In an embodiment, the control unit activates the draw-in mechanism when a sheet reaches a minimum spacing from the stack of sheets.
In an embodiment, a third light barrier disposed in the conveyor and downstream of the second light barrier, the third light barrier for determining the spacing between successive sheets, the third light barrier being connected to the control unit and sending signals thereto, the control unit determining a holding time during which the draw-in mechanism is deactivated, the holding time being dependent on the spacing and on a previously measured draw-in speed, whereby the predetermined spacing exists between successive sheets after expiration of the holding time.
In an embodiment, the method of the invention comprises pulling an outwardly lying first sheet from a stack sheets, transporting the cover sheet at a variable draw-in speed from the stack to a conveyor, and transporting the sheet through the conveyor at a constant conveying speed.
In an embodiment, the draw-in speed is varied periodically.
In an embodiment, the draw-in speed is varied when multiple sheet pulls occur.
In an embodiment, the apparatus of the present invention provides an apparatus for feeding sheet material into a printer or copier that comprises at least one sheet compartment for receiving a sheet stack, a draw-in mechanism for pulling an outwardly lying first sheet from the stack at a draw-in speed, at least one conveyor for conveying the sheet at a conveying speed, and a control unit for controlling the draw-in mechanism wherein the control unit varies the draw-in speed when the pulling the first sheet off of the stack.